1. Field of Invention
The present invention is directed, in general, to borehole production power systems and, more specifically, to powering downhole measurement and control mechanisms using alternating current power over the three phase power cable.
2. Description of Prior Art
Downhole electrical submersible pump (ESP) instrumentation systems are typically powered by impressing a direct current (DC) voltage relative to ground on all three phases of the three phase power cable carrying power to the pump motor. As a result, the normally floating phases of the three phase power system no longer float but are instead maintained at this voltage (on average).
The impressed DC voltage is used to power measurement devices within the borehole and, in most cases, to transmit data back to the surface. However, these direct current systems limit high voltage insulation testing of the three phase cable, and become inoperable if any phase of the three phase power system shorts to ground.
There is, therefore, a need in the art for an improved system for powering downhole instrumentation over a three phase power cable carrying power to a pump motor.